Impulse noise mitigation under out-of-band interference conditions

ABSTRACT

An impulse noise mitigation circuit (INMC) may set a cut-off frequency of each of two high pass filters to bound a frequency bandwidth of a desired signal, wherein a first of the two filters allows frequencies higher than the frequency bandwidth of the desired signal, and a second of the two filters allows frequencies lower than the frequency bandwidth of the desired signal. The INMC may compute and store a mean magnitude separately for a first signal response of the first filter and a second signal response of the second filter. The INMC may select the first filter for impulse noise mitigation when the mean magnitude of the second filter is greater than the mean magnitude of the first filter. The INMC may select the second filter for impulse noise mitigation when the mean magnitude of the first filter is greater than the second filter.

CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.13/941,604 filed on Jul. 15, 2013 and now patented as U.S. Pat. No.8,792,543, which is a continuation of U.S. patent application Ser. No.12/924,185 filed on Sep. 22, 2010, now patented as U.S. Pat. No.8,488,663, which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention is related to a wireless communication receiverand in particular impulse noise mitigation.

2. Description of related art

Noise and in particular impulse noise, which is generated in shortbursts, can be disruptive to data (broadcasts) that are processedthrough an analog receiver and translated into a digital format toproduce a quality output as one might experience in a received radiotransmission. The impulse noise can be caused by many modern day sourcesin which ignition systems and domestic appliances represent a couple ofsources. Elimination or mitigation of impulse noise is essential to aclear reproduction of the received analog signal into a digital signalformat.

US Patent Application Publication 2010/0054150 (Oksman et al.) isdirected to a method and system in which impulse noise is monitored andnoise protection parameters are adjusted. In US Patent ApplicationPublication 2009/0323903 (Cioffi et al.) a method and apparatus isdirected to monitoring and adjusting noise abatement in a DSL link. InUS Patent Application Publication 2009/0168929 (Liu et al.) a method andapparatus is directed to an adaptive impulse noise detection andsuppression. In US Patent Application Publication 2003/0099287(Arambepola) a method and apparatus is directed to detecting impulsenoise in COFDM modulated TV signals.

U.S. Pat. No. 7,676,046 B1 (Nelson et al.) is directed to a method ofremoving noise and interference from a signal by calculating atime-frequency domain of the signal and modifying each instantaneousfrequency. U.S. Pat. No. 7,630,448 B2 (Zhidkov) is directed to a methodto reduce noise in a multiple carrier modulated signal by estimatingimpulse noise and removing the noise as a function of the estimatedimpulse noise. U.S. Pat. No. 7,573,966 B2 (Kim et al.) is directed to asignal conditioning filter and a signal integrity unit to addressequalization and noise filtering to improve signal fidelity. In U.S.Pat. No. 7,558,337 B2 (Ma et al.) a method and apparatus is directed tosignal processing to mitigate impulse noise. In U.S. Pat. No. 7,499,497B2 (Huang et al.) a method and apparatus is directed to suppression ofimpulse noise in an OFDM system. U.S. Pat. No. 7,302,240 B2 (Koga etal.) is directed to a communication apparatus that has an ADC to convertan analog signal to a digital signal before applying an noise detector.

U.S. Pat. No. 7,139,338 B2 (Wilson et al.) is directed to a receiverwith a filter and an impulse response from which a controller adapts theimpulse response to the filter. U.S. Pat. No. 7,035,361 B2 (Kim et al.)is directed to a signal conditioning filter and a signal integrity unitto address coupled problems of equalization and noise filtering. In U.S.Pat. No. 7,016,739 B2 (Bange et al.) a system and method is directed toremoving narrowband from an input signal in which notch frequencies ofnotch filters are adjusted in accordance with a detected noise spectrum.In U.S. Pat. No. 6,920,194 B2 (Stopler et al.) a method and system isdirected to correcting impulse noise present on an input signal. U.S.Pat. No. 6,795,559 B1 (Taura et al.) is directed to an impulse noisereducer, which detects and smoothes impulse noise on an audio signal.U.S. Pat. No. 6,647,070 B1 (Shalvi et al.) is directed to a method andapparatus for combating impulse noise in digital communication channels.U.S. Pat. No. 6,385,261 B1 (Tsuji et al.) is directed to an impulsenoise detector an noise reduction system in an audio signal. U.S. Pat.No. 5,410,264 (Lechleider) is directed to an impulse noise canceller,which recognizes, locates and cancels impulse noise on an incomingsignal. U.S. Pat. No. 5,226,057 (Boren) is directed to adaptive digitalnotch filters for use with RF receivers to reduce interference. U.S.Pat. No. 4,703,447 (Lake, Jr.) is directed to a mixer controlledvariable passband finite impulse response filter. U.S. Pat. No.4,703,447 (Lake, Jr.) is directed to a mixer controlled variablepassband finite impulse response filter.

A primary purpose of a receiving tuner is to select a particular channelof interest and convert that frequency band to a baseband for digitalsignal processing. Shown in FIG. 1 of prior art an output 11 of a tuner10 is processed through an analog to digital converter (ADC) 12 totranslate the analog output 11 of the tuner into a digital time domainwaveform. Mitigation of sudden spikes in the time domain waveform, whichare caused by impulse noise, prevent an accurate demodulation 16 of thedigital signal produced by the ADC 12. The output 13 of the ADC 12 isapplied to an impulse noise mitigation circuit 14 and the output 15 ofthe impulse noise mitigation circuit is connected to a demodulator 16.

Shown in FIG. 2 of prior art is an expansion of the impulse noisemitigation 14 for time domain noise mitigation for impulse noiseinterference detection. An output of a magnitude function 20 is comparedto a threshold using a standard comparator 22. the output 23 of thecomparator 22 is used as an impulse noise flag by the suppressor circuit24. The output of the suppressor circuit 15 is connected to thedemodulator 16. The detection threshold of the comparator 22 can eitherbe a fixed predetermined value or the detection threshold can bedynamically calculated based on the output 21 of the magnitude function.The suppressor circuit 24 either clips the samples of the digital signalthat are found to be impulse noise in the comparator or nulls out thecorrupted samples of the digital signal caused by impulse noise.

A shortcoming of the time domain method of impulse noise mitigation,shown in FIG. 2, is the inability to detect the presence of impulsenoise under normal or relatively high carrier to interference ratio. Theimpulse noise can often be buried under the average envelop of thedesired signal.

FIG. 3 is an impulse noise mitigation scheme of prior art in thefrequency domain. The output of the ADC 13, shown in FIG. 1, isconnected to a high pass filter 30 and the output 31 of the high passfilter is connected to a magnitude function 32. The output of themagnitude function 33 is applied to a comparator circuit 34 having adetection threshold control. The output 35 of the comparator isconnected to a suppressor circuit 36, which connects 15 back to thedemodulator shown in FIG. 1

In the scheme shown in FIG. 3 the detection threshold can be fixed to apredetermined value or dynamically adjusted based on the output 33 ofthe magnitude function 32. The suppressor circuit 36 either clips thesignal samples that are determined to be impulse noise or nulls out thecorrupted samples.

The main drawback of the frequency domain method shown in FIG. 3 is theinability to detect the presence of impulse noise under out of bandinterferers, especially adjacent interferers, where the signal at theoutput of the magnitude function 33 will contain the energy of both theimpulse noise and the interferers thus making the detection of impulsenoise unreliable.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide two complexfilters to improve the frequency domain impulse mitigation.

It is still an objective of the present invention wherein a first filteradmits only frequency components higher than the desired signalbandwidth in the positive frequency domain and the second filter admitsfrequency components lower than the desired signal bandwidth in thenegative frequency domain.

It is further an objective of the present invention to measure the meanmagnitude over a time interval T of each of the two high pass filters inorder to select which of the two filters to use to detect and mitigateimpulse noise.

In the present invention two complex high pass filters are used tomitigate impulse noise and other noise interferer signals. The responseof each individual filter is measured over a time period T to determinewhich filter provides the best response. This measurement is the meanmagnitude of the noise signal that is being removed from the signalbeing connected to the output of an impulse noise mitigation circuit,whereupon the filter producing the lowest mean magnitude value is chosenfor impulse noise mitigation. This selection also dramatically reducesenergy of other noise interferer signals. It should be noted that one ofthe two filters admits frequency components higher than the desiredbandwidth on the positive frequency axis and the other of the twofilters only admits frequency components lower than the desired signalbandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described with reference to the accompanyingdrawings, wherein:

FIG. 1 is a block diagram of a typical communication receiver of priorart;

FIG. 2 is a block diagram of time domain impulse noise mitigation ofprior art;

FIG. 3 is a block diagram of frequency domain impulse noise mitigationof prior art;

FIG. 4 is a block diagram of the present invention of frequency domainimpulse noise mitigation;

FIG. 5 is a frequency domain diagram showing the effects of the impulsenoise mitigation relative to the desired signal, and

FIG. 6 is a method for impulse noise mitigation of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 4 is shown a block diagram of the frequency domain impulse noisemitigation 40 of the present invention. The output of an analog tuner 41is connected to an ADC 42 to convert the receiver analog signal into adigital signal. The output 43 of the ADC 42 is coupled to the impulsenoise mitigation circuit 40 for the purpose of impulse noise detection.The output of the ADC 43 is also connected to the suppressor circuit 57.When impulse noise is detected from signal samples applied to thefilters 44 and 48, these samples will be flagged with an impulse noiseindicator, and then the mitigation is applied to the corresponding ADCoutput connected directly to the suppressor circuit 57.

Within the impulse noise mitigation circuitry 40 are two complex highpass filters 44 and 48, filter 1 and filter 2 respectively. Each offilter output is connected to a magnitude function 45 and 49,respectively, in which outputs of the magnitude functions are connectedto accumulator circuits 46 and 50, respectively. After accumulation overT samples, filter selection 52 selects one of Filter1 44 and Filter2 48by comparing accumulator outputs 47 and 51. The unselected filter can bedisabled hereafter to reduce power consumption. The selected filteroutput is connected to a magnitude, or gain, function 55 that isconnected to a comparator 56. A detection threshold is either a fixed toa predetermined value, or dynamically adjusted based on the output ofthe magnitude function 55. The suppressor circuit 57 connects the noisemitigated signal to the demodulator 58 and either clips the signalsamples that are determined to be impulse noise, or nulls out thecorrupted samples. A state machine 59 controls the operation of theimpulse noise mitigation circuitry 40, including which filter toactivate, evaluation of the mean magnitude over T samples for eachfilter and the filter chosen to mitigate the impulse noise and anyinterferers.

It should be noted that it is within the scope of the present inventionthat a single programmable filter can be used, wherein both filters areintegrated together and are separately selectable. The programmablefilter is first configured similar to filter1 44 and the mean magnitudeu1 is measured over T samples. Then the programmable filter isconfigured similar to filter2 48 and the mean magnitude u2 is measuredover T samples. The two mean magnitudes u1 and u2 are compared, and theprogrammable filter is configured according to the method shown in FIG.6.

It should also be noted that by using only one filter and disabling theother filter, power consumption can be improved. The purpose of usingtwo filters is to detect impulse noise under out-of-band interferenceconditions, which is a drawback of the prior art shown in FIG. 3. Thusthe present invention improves impulse noise detection by selecting afilter without out-of-band interference.

FIG. 5 demonstrates the effects of the two complex high pass filters ofthe impulse noise mitigation method of the present invention in thefrequency domain. Filter1 only allows frequency components higher thanthe cut-off frequency of filter1 to pass through the impulse noisemitigation circuit 40 and filter2 only allows frequency components lowerthan the cut-off frequency of filter2 to pass through the impulse noisemitigation circuit. By collecting the mean signal data over a timeduration (or samples) T for each filter the state machine 59 selectswhich filter to use to detect impulse noise under significantout-of-band interference condition.

FIG. 6 demonstrates the method for impulse noise mitigation of thepresent invention. Under control of the state machine 59 the response ofthe first filter to impulse noise and other interferer frequencies ismeasured 60. The mean magnitude (u1) of the effects on the incomingsignal is computed and stored for the first filter 61 over a timeduration (or sample) of “T”. Then the response of the second filter toimpulse noise and other interferers is measured 62, and the meanmagnitude (u2) of the effects on the incoming signal is computed andstore for the second filter 63 over a time (or sample) duration of “T”.If the computed mean value “u2” is greater than the computed mean value“u1” 64, then the first filter is selected and used for impulse noisedetection and mitigation 65. Otherwise if “u1” is greater than or equalto “u2” 66, the second filter is selected and used for impulse noisedetection and mitigation 65. The unselected filter can be disabledhereafter to reduce power consumption.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

What is claimed is:
 1. A system comprising: one or more filtersconfigurable to have a first high-pass response and a second high-passresponse, a signal magnitude determination circuitry, a comparator, anda filter response selection circuitry, wherein: said signal magnitudedetermination circuity is operable to measure mean magnitude, over adetermined time interval, of a signal processed using said firsthigh-pass response; said signal magnitude determination circuity isoperable to measure mean magnitude, over a determined time interval, ofa signal processed using said second high-pass response; and said filterresponse selection circuitry is operable to select which of said firsthigh-pass response and said second high-pass response to use forsuppression of impulse noise in a received signal; said comparator isoperable to compare a first signal to an impulse noise detectionthreshold; and said first signal is a result of processing of saidreceived signal by said one or more filters configured to have theselected one of: said first high-pass response, and said secondhigh-pass response.
 2. The system of claim 1, comprising a suppressorcircuit that is operable to clip or null samples of said received signalto generate a suppressor circuit output signal.
 3. The system of claim2, wherein an output of said comparator controls said suppressorcircuit.
 4. The system of claim 1, wherein said signal magnitudedetermination circuitry comprises: first signal magnitude determinationcircuitry used to control said filter response selection circuitry; andsecond signal magnitude determination circuitry used for determining amagnitude of said received signal.
 5. The system of claim 1, wherein acutoff frequency of said first high-pass response is higher than alowest desired frequency of said received signal.
 6. The system of claim1, wherein a cutoff frequency of said second high-pass response is lowerthan a lowest desired frequency of said received signal.
 7. The systemof claim 1, wherein said selection is based on: said measured meanmagnitude of said signal processed using said first high-pass response;and said measured mean magnitude of said signal processed using saidsecond high-pass response.
 8. A method comprising: in a receivercomprising one or more filters configurable to have a first high-passresponse and a second high-pass response, a signal magnitudedetermination circuitry, a comparator, and a filter response selectioncircuitry: measuring, by said signal magnitude determination circuity,mean magnitude, over a determined time interval, of a signal processedusing said first high-pass response; measuring, by said signal magnitudedetermination circuity, mean magnitude, over a determined time interval,of a signal processed using said second high-pass response; andselecting, by said filter response selection circuitry, which of saidfirst high-pass response and said second high-pass response to use forsuppression of impulse noise in a received signal; generating a firstsignal by processing said received signal using said one or more filtersconfigured to have the selected one of: said first high-pass response,and said second high-pass response; and comparing said first signal toan impulse noise detection threshold.
 9. The method of claim 8, whereinsaid receiver comprises a suppressor circuit, and said suppressorcircuit clips or nulls samples of said received signal to generate asuppressor circuit output signal.
 10. The method of claim 9, comprisingcontrolling said clipping or nulling via an output of said comparator.11. The method of claim 8, wherein: said signal magnitude determinationcircuitry comprises first signal magnitude determination circuitry andsecond signal magnitude determination circuitry; said first signalmagnitude determination circuitry determines a magnitude of saidreceived signal; and said second signal magnitude determinationcircuitry controls said filter response selection circuitry.
 12. Themethod of claim 8, wherein a cutoff frequency of said first high-passresponse is higher than a lowest desired frequency of said receivedsignal.
 13. The method of claim 8, wherein a cutoff frequency of saidsecond high-pass response is lower than a lowest desired frequency ofsaid received signal.
 14. The method of claim 8, comprising: performingsaid selecting based on: said measured mean magnitude of said signalprocessed using said first high-pass response; and said measured meanmagnitude of said signal processed using said second high-pass response.15. A system comprising: one or more filters configurable to have afirst high-pass response and a second high-pass response, a signalmagnitude determination circuitry, and a filter response selectioncircuitry, wherein: said signal magnitude determination circuity isoperable to measure mean magnitude, over a determined time interval, ofa signal processed using said first high-pass response; said signalmagnitude determination circuity is operable to measure mean magnitude,over a determined time interval, of a signal processed using said secondhigh-pass response; and said filter response selection circuitry isoperable to select which of said first high-pass response and saidsecond high-pass response to use for suppression of impulse noise in areceived signal; said selection is based on: said measured meanmagnitude of said signal processed using said first high-pass response;and said measured mean magnitude of said signal processed using saidsecond high-pass response; and said selection is such that: said firsthigh-pass response is selected when said measured mean magnitude of saidsignal processed using said first high-pass response is less than saidmeasured mean magnitude of said signal processed using said secondhigh-pass response; and said second high-pass response is selected whensaid measured mean magnitude of said signal processed using said firsthigh-pass response is greater than said measured mean magnitude of saidsignal processed using said second high-pass response.
 16. The system ofclaim 15, wherein: a cutoff frequency of said first high-pass responseis higher than a lowest desired frequency of said received signal; and acutoff frequency of said second high-pass response is lower than alowest desired frequency of said received signal.
 17. A methodcomprising: in a receiver comprising one or more filters configurable tohave a first high-pass response and a second high-pass response, asignal magnitude determination circuitry, a comparator, a suppressorcircuit, and a filter response selection circuitry: measuring, by saidsignal magnitude determination circuity, mean magnitude, over adetermined time interval, of a signal processed using said firsthigh-pass response; measuring, by said signal magnitude determinationcircuity, mean magnitude, over a determined time interval, of a signalprocessed using said second high-pass response; selecting, by saidfilter response selection circuitry, which of said first high-passresponse and said second high-pass response to use for suppression ofimpulse noise in a received signal; comparing, by said comparator, afirst signal to an impulse noise detection threshold, said first signalis a result of processing of said received signal by said one or morefilters configured to have the selected one of: said first high-passresponse and said second high-pass response; and clipping or nulling, bysaid suppressor circuit, samples of said received signal to generate asuppressor circuit output signal; and controlling said clipping ornulling via an output of said comparator.
 18. The method of claim 17,wherein: a cutoff frequency of said first high-pass response is higherthan a lowest desired frequency of said received signal; and a cutofffrequency of said second high-pass response is lower than a lowestdesired frequency of said received signal.
 19. A method comprising: in areceiver comprising one or more filters configurable to have a firsthigh-pass response and a second high-pass response, a signal magnitudedetermination circuitry, a comparator, and a filter response selectioncircuitry: measuring, by said signal magnitude determination circuity,mean magnitude, over a determined time interval, of a signal processedusing said first high-pass response; measuring, by said signal magnitudedetermination circuity, mean magnitude, over a determined time interval,of a signal processed using said second high-pass response; andselecting, by said filter response selection circuitry, which of saidfirst high-pass response and said second high-pass response to use forsuppression of impulse noise in a received signal, wherein: saidselecting is based on: said measured mean magnitude of said signalprocessed using said first high-pass response; and said measured meanmagnitude of said signal processed using said second high-pass response;and said selecting is such that: said first high-pass response isselected when said measured mean magnitude of said signal processedusing said first high-pass response is less than said measured meanmagnitude of said signal processed using said second high-pass response;and said second high-pass response is selected when said measured meanmagnitude of said signal processed using said first high-pass responseis greater than said measured mean magnitude of said signal processedusing said second high-pass response.
 20. The method of claim 19,wherein: a cutoff frequency of said first high-pass response is higherthan a lowest desired frequency of said received signal; and a cutofffrequency of said second high-pass response is lower than a lowestdesired frequency of said received signal.